The present invention relates to an in-pipe work apparatus which moves inside a pipe by itself and carries out an inspection of the pipe or jobs such as welding-cutting, and repairing.
An in-pipe work apparatus is used for works in a pipe in an atomic power plant, a chemical plant, and the like and in other general industrial fields. This kind of in-pipe work apparatus is applied to a wide range including an inspection on inner walls of a pipe, cleaning (such as removal of foreign matters) thereof, welding and cutting, an inspection on a welded portion, and the like. The kinds of pipes which can be dealt with by this apparatus range variously. Due to limitations from diameters of pipe, the structure of an in-pipe work apparatus is arranged so as to integrate a movement device and a work device together, in some cases, or is arrange such that both devices are separated from each other.
A pipe as a work target to be dealt with normally has a pipe length which is several hundreds times longer than the inner diameter of the pipe itself, and includes a bending portion or a branch portion. Therefore, it is necessary for an in-pipe work apparatus moving in a pipe to be capable of responding to various moving patterns including forward and backward movements, lateral movements in left and right directions, vertical movements in the upward and downward directions, and the like.
In addition, an in-pipe work apparatus is connected to an external control apparatus outside the pipe, by cables and hoses. Examples of the cables and hoses connected to the control apparatus are metal cables or optical fiber cables. A metal cable, a hydraulic hose, or the like is used for power transmission. Such a cable or hose includes a number of cores. Since these cables and hoses a tension load when moving, in many cases, cables and hoses are used in form of a composite cable added with a tension member (or a tension cable) in view of conveniences of handling inside and outside a pipe.
However, if cables and hoses are shaped into one composite cable, the outer size, weight, and tolerable bending diameter are enlarged, and the bending reaction force is accordingly increased greatly. Therefore, there is a risk that a composite cable cannot be smoothly guided into a pipe or a composite cable is difficult to be wound up by a cable winding apparatus.
Although an in-pipe work apparatus comprises a movement device which makes the apparatus run in a pipe, this movement device must generate a tractive force large enough to smoothly move various component devices and the work apparatus with the composite cable connected thereto. Mechanisms of a wheel type, a crawler type, a spiral type, a spanworm type, and the like have been designed and are being put into practical use.
Further, since an in-pipe work apparatus moves with a composite cable drawing together in a pipe, a friction resistance is generated between the inner wall of the pipe and the composite cable. In addition, a loss of a tension force is caused at a curved pipe portion of the pipe since the direction of the tension changes at this curved pipe portion, so that the friction resistance is increased. When a pipe as a target to be dealt with has a long pipe path and includes a number of curved portions, the tractive force required for the movement device is extremely large. Therefore, how the friction between the inner wall and the composite cable can be reduced is a significant problem to smoothly accomplish moving and works inside a pipe.
In addition, since the in-pipe work apparatus must moves inside a pipe, the shape of the in-pipe work apparatus naturally depends on the pipe diameter of a pipe as a target to be dealt with and shapes of curved portions thereof. If the pipe diameter and the curvatures of bending portions are small, the effective cross-section area is small so that the movement device and the work apparatus must shaped to be narrow and long.
Thus, there has been a demand for a movement device which is capable of accurately detecting the moving position of itself and securely moving in a pipe under conditions as described above.